1. Field of the Invention
The present invention relates to a semiconductor integrated circuit, and particularly to improvement in a cell structure primarily used in the automatic placement and routing in the layout design of a semiconductor integrated circuit.
2. Description of Related Art
FIG. 8 is a plan view showing a cell structure used for designing a conventional semiconductor integrated circuit. In FIG. 8, the reference numeral 100 designates a cell, which is an inverter in this case. The reference numeral 101 designates a power supply trunk placed in the cell 100, and 102 designates a ground trunk placed in the cell 100. The reference numeral 103 designates a metal line of the source electrode of a PMOSFET placed at a power supply side; and 104 designates a contact connecting the metal line 103 to the active region 105 of the PMOSFET. The metal line 103 is also connected to the power supply trunk 101. The reference numeral 106 designates the active region of an NMOSFET; and 107 designates a metal line of the source electrode of the NMOSFET placed on the ground side. The metal line 107 is connected to the active region 106 via the contacts 104. The reference numeral 108 designates a gate electrode of the PMOSFET; 109 designates a gate electrode of the NMOSFET; and 110 designates a metal line for interconnecting the gate electrodes 108 and 109. The metal line 110 functions as an input pin of the inverter. The reference numeral 111 designates a metal line at the output side; and 112 designates a contact for connecting the metal line 111 to the active regions 105 and 106.
Next, the outline of the conventional cell will be described.
As shown in FIG. 8, the cell used for the conventional automatic placement and routing is configured such that the power supply trunk 101 is connected to the metal line 103 of the source electrode on the power supply side in advance, and the ground trunk 102 is connected to the metal line 107 of the source electrode on the ground side in advance. Thus, the cell 100 constituting the inverter operates at the power supply potential fed via the power supply trunk 101.
When a plurality of cells 100 are automatically placed adjacently, the cells 100 are connected to the power supply trunk 101 and ground trunk 102 that supply the common potential because of the routing structure described above. Accordingly, two adjacent cells 100 are connected in common to the power supply and ground with the same potentials without exception.
With the configuration as described above, the conventional semiconductor integrated circuit has the following problem. Because the power supply trunk 101 is connected to the metal line 103 of the source electrode on the power supply side, and the ground trunk 102 is connected to the metal line 107 of the source electrode on the ground side within the cell 100 in advance, and hence the power supply trunk and ground trunk are used in common, it is unavoidable that the adjacent cells 100 have the same potential. Accordingly, it is impossible to connect the power supplies with different potentials to the adjacent cells 100. As a result, to control the power supply voltage individually for each cell 100, the cells 100 that are connected to power supplies with different potentials must be separated, thereby complicating the layout.
The present invention is implemented to solve the foregoing problem. It is therefore an object of the present invention to provide a semiconductor integrated circuit capable of connecting the adjacent cells to a plurality of power supplies with different potentials.
According to one aspect of the present invention, there is provided a semiconductor integrated circuit including cells and potential feeders. Each cell includes a partial trunk which is used to constitute a power supply trunk and/or ground trunk, and is electrically isolated from remaining components within the cell. The potential feeders are selectively connected to the power supply trunk and/or ground trunk of any one of cell rows, and supply the components within the cells with a potential fed via the power supply trunk and/or ground trunk. Thus, the semiconductor integrated circuit can supply the adjacent cells with different potentials, thereby offering an advantage of being able to control the potentials to be supplied to the cells on a cell by cell basis with ease.